Epitaxy is a process that is used extensively in semiconductor processing to form very thin material layers on semiconductor substrates. These layers frequently define some of the smallest features of a semiconductor device, and they may have a high quality crystal structure if the electrical properties of crystalline materials are to be controlled. A deposition precursor is normally provided to a processing chamber in which a substrate is disposed. The substrate is then heated to a temperature that favors growth of a material layer having particular properties.
During epitaxy, the films produced usually have very uniform thickness, composition, and structure. Because of variations in local substrate temperature, gas flows, and precursor concentrations, it is quite challenging to form films having uniform and repeatable properties. The processing chamber is normally a vessel capable of maintaining high vacuum, typically below 10 Torr, and heat is normally provided by heat lamps positioned outside the vessel to avoid introducing contaminants. Control of substrate temperature, and therefore of local layer formation conditions, is complicated by thermal absorptions and emissions of chamber components and exposure of sensors and chamber surfaces to film forming conditions inside the processing chamber. There remains a need for an epitaxy chamber with improved temperature control, and methods of operating such a chamber to improve uniformity and repeatability.